I have the same “problem”.
I am using actual WordPress-, Woocommerce- and Symbiostock-Versions, I am currently building a new site to market my old slides.
It does not seem to affect the performance of the site.
It is for sure the plugin symbiostock pro that causes the error, when I disable this plugin I don’t get any error messages anymore.
Even though there are no problems in everyday life, I can understand that my colleagues are getting nervous and would be happy if they wouldn’t have to see this error on every check.
Nevertheless, thanks for the work, a really very good plugin, I think I will go online in a few days with my site stock-analog.com.